Gastrointestinal Tract: Fat Metabolism in the Colon

Abstract

Lipids in colonic digesta are derived from the undigested residue of dietary fat and partly from endogenous secretions and shedding of colonocytes. Generally, only a small proportion of dietary fat consumed by man reaches the large intestine. Studies in mice have shown that high-fat diets alter the composition and function of the gastrointestinal (GI) microbiota, though nonequivalent control diets confound these findings. While a western-style diet, high in fats and refined carbohydrates, is associated with obesity and detrimental health effects, the explicit effects of high-fat diets on the human gut microbiota are poorly understood. Some clinical conditions result in increased fluxes of lipids to the large intestine, and, increasingly, slimming drugs that inhibit pancreatic lipases or adsorbents, including fatty acid-adsorbing Lactobacillus spp., that enable fat to bypass the small intestine also result in large quantities of dietary lipids reaching the colon. GI bacterial lipases and phospholipases release fatty acids and various glycerides that may then be metabolized further to form products that have implications for GI health. The bacterial species responsible for lipase activity in the human colon are poorly characterized.